avfilter/avf_showvolume: fix several issues

Fix color fading: previously color could fade to red when
volume level for red color was actually never reached.
Display volume value on right side.
Use red color only if clipping is needed.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -14302,13 +14302,13 @@ Set video rate.
 Set border width, allowed range is [0, 5]. Default is 1.
 
 @item w
-Set channel width, allowed range is [40, 1080]. Default is 400.
+Set channel width, allowed range is [80, 1080]. Default is 400.
 
 @item h
 Set channel height, allowed range is [1, 100]. Default is 20.
 
 @item f
-Set fade, allowed range is [1, 255]. Default is 20.
+Set fade, allowed range is [0.001, 1]. Default is 0.95.
 
 @item c
 Set volume color expression.
@@ -14325,6 +14325,9 @@ Current channel number, starting from 0.
 
 @item t
 If set, displays channel names. Default is enabled.
+
+@item v
+If set, displays volume values. Default is enabled.
 @end table
 
 @section showwaves

libavfilter/avf_showvolume.c

@@ -18,6 +18,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/avstring.h"
 #include "libavutil/channel_layout.h"
 #include "libavutil/eval.h"
 #include "libavutil/intreadwrite.h"
@@ -30,16 +31,22 @@
 #include "video.h"
 #include "internal.h"
 
+static const char *const var_names[] = {   "VOLUME",   "CHANNEL",        NULL };
+enum                                   { VAR_VOLUME, VAR_CHANNEL, VAR_VARS_NB };
+
 typedef struct ShowVolumeContext {
     const AVClass *class;
     int w, h;
-    int f, b;
+    int b;
+    double f;
     AVRational frame_rate;
     char *color;
 
     AVFrame *out;
     AVExpr *c_expr;
     int draw_text;
+    int draw_volume;
+    double *values;
 } ShowVolumeContext;
 
 #define OFFSET(x) offsetof(ShowVolumeContext, x)
@@ -49,19 +56,17 @@ static const AVOption showvolume_options[] = {
     { "rate", "set video rate",  OFFSET(frame_rate), AV_OPT_TYPE_VIDEO_RATE, {.str="25"}, 0, 0, FLAGS },
     { "r",    "set video rate",  OFFSET(frame_rate), AV_OPT_TYPE_VIDEO_RATE, {.str="25"}, 0, 0, FLAGS },
     { "b", "set border width",   OFFSET(b), AV_OPT_TYPE_INT, {.i64=1}, 0, 5, FLAGS },
-    { "w", "set channel width",  OFFSET(w), AV_OPT_TYPE_INT, {.i64=400}, 40, 1080, FLAGS },
+    { "w", "set channel width",  OFFSET(w), AV_OPT_TYPE_INT, {.i64=400}, 80, 1080, FLAGS },
     { "h", "set channel height", OFFSET(h), AV_OPT_TYPE_INT, {.i64=20}, 1, 100, FLAGS },
-    { "f", "set fade",           OFFSET(f), AV_OPT_TYPE_INT, {.i64=20}, 1, 255, FLAGS },
-    { "c", "set volume color expression", OFFSET(color), AV_OPT_TYPE_STRING, {.str="if(gte(VOLUME,-2), if(gte(VOLUME,-1),0xff0000ff, 0xff00ffff),0xff00ff00)"}, 0, 0, FLAGS },
+    { "f", "set fade",           OFFSET(f), AV_OPT_TYPE_DOUBLE, {.dbl=0.95}, 0.001, 1, FLAGS },
+    { "c", "set volume color expression", OFFSET(color), AV_OPT_TYPE_STRING, {.str="if(gte(VOLUME,-6), if(gte(VOLUME,-2), if(gte(VOLUME,-1), if(gt(VOLUME,0), 0xff0000ff, 0xff0066ff), 0xff00ffff),0xff00ff00),0xffff0000)"}, 0, 0, FLAGS },
     { "t", "display channel names", OFFSET(draw_text), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS },
+    { "v", "display volume value", OFFSET(draw_volume), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS },
     { NULL }
 };
 
 AVFILTER_DEFINE_CLASS(showvolume);
 
-static const char *const var_names[] = {   "VOLUME",   "CHANNEL",        NULL };
-enum                                   { VAR_VOLUME, VAR_CHANNEL, VAR_VARS_NB };
-
 static av_cold int init(AVFilterContext *ctx)
 {
     ShowVolumeContext *s = ctx->priv;
@@ -116,7 +121,9 @@ static int config_input(AVFilterLink *inlink)
     inlink->partial_buf_size =
     inlink->min_samples =
     inlink->max_samples = nb_samples;
-
+    s->values = av_calloc(inlink->channels * VAR_VARS_NB, sizeof(double));
+    if (!s->values)
+        return AVERROR(ENOMEM);
     return 0;
 }
 
@@ -162,7 +169,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
     AVFilterLink *outlink = ctx->outputs[0];
     ShowVolumeContext *s = ctx->priv;
     int c, i, j, k;
-    double values[VAR_VARS_NB];
+    AVFrame *out;
 
     if (!s->out || s->out->width  != outlink->w ||
                    s->out->height != outlink->h) {
@@ -181,10 +188,10 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
     for (j = 0; j < outlink->h; j++) {
         uint8_t *dst = s->out->data[0] + j * s->out->linesize[0];
         for (k = 0; k < s->w; k++) {
-            dst[k * 4 + 0] = FFMAX(dst[k * 4 + 0] - s->f, 0);
-            dst[k * 4 + 1] = FFMAX(dst[k * 4 + 1] - s->f, 0);
-            dst[k * 4 + 2] = FFMAX(dst[k * 4 + 2] - s->f, 0);
-            dst[k * 4 + 3] = FFMAX(dst[k * 4 + 3] - s->f, 0);
+            dst[k * 4 + 0] = FFMAX(dst[k * 4 + 0] * s->f, 0);
+            dst[k * 4 + 1] = FFMAX(dst[k * 4 + 1] * s->f, 0);
+            dst[k * 4 + 2] = FFMAX(dst[k * 4 + 2] * s->f, 0);
+            dst[k * 4 + 3] = FFMAX(dst[k * 4 + 3] * s->f, 0);
         }
     }
 
@@ -196,10 +203,10 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
         for (i = 0; i < insamples->nb_samples; i++)
             max = FFMAX(max, src[i]);
 
+        s->values[c * VAR_VARS_NB + VAR_VOLUME] = 20.0 * log10(max);
         max = av_clipf(max, 0, 1);
-        values[VAR_VOLUME] = 20.0 * log10(max);
-        values[VAR_CHANNEL] = c;
-        color = av_expr_eval(s->c_expr, values, NULL);
+        s->values[c * VAR_VARS_NB + VAR_CHANNEL] = c;
+        color = av_expr_eval(s->c_expr, &s->values[c * VAR_VARS_NB], NULL);
 
         for (j = 0; j < s->h; j++) {
             uint8_t *dst = s->out->data[0] + (c * s->h + c * s->b + j) * s->out->linesize[0];
@@ -214,8 +221,21 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
     }
 
     av_frame_free(&insamples);
+    out = av_frame_clone(s->out);
+    if (!out)
+        return AVERROR(ENOMEM);
+    av_frame_make_writable(out);
+
+    for (c = 0; c < inlink->channels && s->draw_volume; c++) {
+        if (s->h >= 8) {
+            char buf[16];
+
+            snprintf(buf, sizeof(buf), "%.2f", s->values[c * VAR_VARS_NB + VAR_VOLUME]);
+            drawtext(out, FFMAX(0, s->w - 8 * strlen(buf)), c * (s->h + s->b) + (s->h - 8) / 2, buf);
+        }
+    }
 
-    return ff_filter_frame(outlink, av_frame_clone(s->out));
+    return ff_filter_frame(outlink, out);
 }
 
 static av_cold void uninit(AVFilterContext *ctx)
@@ -224,6 +244,7 @@ static av_cold void uninit(AVFilterContext *ctx)
 
     av_frame_free(&s->out);
     av_expr_free(s->c_expr);
+    av_freep(&s->values);
 }
 
 static const AVFilterPad showvolume_inputs[] = {